Poly(aryl ether sulfones) have been known for about two decades. They are tough linear polymers that possess a number of attractive features such as excellent high temperature resistance, good electrical properties, and very good hydrolytic stability. At least three poly(aryl ether sulfones) are commercially available. A poly(aryl ether sulfone) referred to herein as poly(phenylene ether sulfone) is available from Imperial Chemical Industries, Ltd. It has the formula (1) ##STR1## and is produced by the polycondensation of 4,4'-dihydroxydiphenyl sulfone with 4,4'-dichlorodiphenyl sulfone as described in, for example, Canadian Patent No. 847,963. The polymer contains no aliphatic moieties and has a Tg of approximately 220.degree. C.
Another commercial poly(aryl ether sulfone) is available from Amoco Performance Products, Inc., under the trademark of UDEL.RTM.. It corresponds to formula (2), ##STR2## has a Tg of about 190.degree. C., and is made via the nucleophilic polycondensation of bisphenol-A di-sodium salt with 4,4'-dichlorodiphenyl sulfone, as described in U.S. Pat. No. 4,108,837.
A third commercial poly(aryl ether sulfone) is also available from Amoco Performance Products, Inc., under the trademark of Radel.RTM. R. It corresponds to formula (3) has a Tg of about 220.degree. C., and is produced by the polycondensation of biphenol with 4,4'-dichlorodiphenyl sulfone as described in, for example, Canadian Patent No. 847,963. ##STR3##
Over the years, there has developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ether sulfones and other poly(aryl ethers) (all hereinafter called "PAE"). A broad range of PAE's was achieved by Johnson et. al., J. of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's.
Because of their excellent mechanical and thermal properties, coupled with outstanding hydrolytic stability, the poly(aryl ether sulfones) have been utilized in the medical market for a variety of purposes for at least ten years. These medical devices constitute a wide variety of articles. Obviously, one of the major attributes of the poly(aryl ether sulfones) is their ability to be steam autoclaved repeatedly without loss of properties. Steam autoclaving is a very severe test, requiring both high temperature and hydrolytic stability, and involving cyclical effects--wet/dry, hot/cold.
The poly(aryl ether sulfones) (1) and (2) show some important deficiencies, however. Indeed, parts molded from these materials, stress-crack when steam sterilized under stresses of say 500 psi or greater especially when excessive concentration of boiler additives, such as morpholine are employed to reduce corrosion in the steam generating system; or, when in contact with commonly used hospital cleaners and detergents.
While poly(biphenyl ether sulfone) (3) and parts molded therefrom have substantially better properties than poly(aryl ether sulfones) (1) and (2) it is substantially more expensive than (1) and (2) due to the high cost of biphenol.
British Patent Application No. 2,088,396 describes copolymers containing units (4) and (5): ##STR4##
The claimed copolymers comprise about 80 to 10 mole percent of repeat units (4), and correspondingly about 20 to 90 mole percent of repeat units (5). The application states that the incorporation of (5) into the poly(aryl ether sulfone) (1) yields materials with improved resistance to hot water crazing. The application does not mention steam-sterilizability under load; nor does it teach that the copolymers show resistance to stress-cracking in the presence of boiler additives such as morpholine.
The general object of this invention is to provide blends of poly(biphenyl ether sulfones) having many of the base properties of the poly(biphenyl ether sulfone). Another object of this invention is to provide medical articles from blends of poly(biphenyl ether sulfones) which can be steam-sterilized while under stresses of 500 psi or greater without stress-cracking even in the presence of morpholine. Other objects appear hereinafter.
The general objects of this invention can be attained with immiscible blends comprising (a) from about 25 to about 99 percent by weight of a poly(biphenyl ether sulfone) and (b) from about 1 to 75 percent by weight of a poly(phenylene ether sulfone). Other things being equal blends of polyarylether (1) and poly(aryl ether sulfone) (3) wherein poly(aryl ether sulfone) (3) comprises at least 60% of the two polymers have substantially the same properties as the more expensive poly(aryl ether sulfone) (3). The two polymers can also be used in weight percent ratios of poly(biphenyl ether sulfone) of from about 50 to 99 to poly(phenylene ether sulfone) of about 50 to 1 weight percent.
Briefly, the poly(biphenyl ether sulfones) useful in this invention comprise the repeating unit ##STR5## wherein at least 50 and preferably at least 75 mole percent of the divalent Ar groups are p-biphenylene groups and the remainder (0 to 50 mole percent) at least one member selected from the group consisting of p-phenylene, ##STR6## etc. In general, the higher the concentration of biphenyl or biphenylene groups the better the properties of the polymer.
The poly(phenylene ether sulfones) useful in this invention comprise the repeating unit ##STR7## wherein at least 50 and preferably at least 75 mole percent of the divalent Ar' groups are bisphenol S moieties ##STR8## and the remainder (0 to 50 mole percent) p-phenylene.
The poly(aryl ether sulfones) can be prepared by either of two methods, i.e., the carbonate method or the alkali metal hydroxide method.
In the carbonate method, the polymers are prepared by contacting substantially equimolar amounts of the hydroxy-containing compounds and dihalodiarylsulfones, e.g., 4,4'-dichlorodiphenyl sulfone or 4,4'-difluorodiphenyl sulfone, with from about 0.5 to about 1.0 mole of an alkali metal carbonate per mole of hydroxyl group in a solvent mixture comprising a solvent which forms an azeotrope with water in order to maintain the reaction medium at substantially anhydrous conditions during the polymerization.
The temperature of the reaction mixture is kept at about 170.degree. C. to about 250.degree. C., preferably from about 210.degree. C. to about 235.degree. C. for about one to 15 hours.
The reaction is carried out in an inert atmosphere, e.g., nitrogen, at atmospheric pressure, although higher or lower pressures may also be used.
The polyarylethersulfone is then recovered by conventional techniques such as coagulation, solvent evaporation, and the like.
The solvent mixture comprises a solvent which forms an azeotrope with water and a polar aprotic solvent. The solvent which forms an azeotrope with water includes an aromatic hydrocarbon such as benzene, toluene, xylene, ethylbenzene, chlorobenzene, and the like.
The polar aprotic solvents employed in this invention are those generally known in the art for the manufacture of polyarylether sulfones and include sulfur containing solvents such as those of the formula: EQU R.sub.1 --S(O).sub.b --R.sub.1
in which each R.sub.1 represents a monovalent lower hydrocarbon group free of aliphatic unsaturation, which preferably contains less than about 8 carbon atoms or when connected together represents a divalent alkylene group with b being an integer from 1 to 2 inclusive. Thus, in all of these solvents, all oxygens and two carbon atoms are bonded to the sulfur atom. Contemplated for use in this invention are such solvents as those having the formula: ##STR9## where the R.sub.2 groups are independently lower alkyl, such as methyl, ethyl, propyle, butyl, and like groups, and aryl groups such as phenyl and alkylphenyl groups such as the tolyl group, as well as those where the R.sub.2 groups are interconnected as in a divalent alkylene bridge such as ##STR10## in tetrahydrothiophene oxides and dioxides. Specifically, these solvents include dimethylsulfoxide, dimethylsulfone, diphenylsulfone, diethylsulfoxide, diethylsulfone, diisopropylsulfone, tetrahydrothiophene 1,1-dioxide (commonly called tetramethylene sulfone or sulfolane) and tetrahydrothiophene-1 monoxide.
Additionally, nitrogen containing solvents may be used. These include dimethylacetamide, dimethylformamide and N-methylpyrrolidone.
The azeotrope forming solvent and polar aprotic solvent are used in a weight ratio of from about 1:10 to about 1:1, preferably from about 1:5 to about 1:3.
In the reaction, the hydroxy containing compound is slowly converted, in situ, to the alkali salt thereof by reacting with the alkali metal carbonate. The alkali metal carbonate is preferably potassium carbonate. As indicated before, mixtures of carbonates such as potassium and sodium carbonate may also be used.
Water is continuously removed from the reaction mass as an azeotrope with the azeotrope forming solvent so that substantially anhydrous conditions are maintained during the polymerization.
It is essential that the reaction medium be maintained substantially anhydrous during the polycondensation. While amounts of water up to about one percent can be tolerated, and are somewhat beneficial when employed with fluorinated dihalobenzenoid compounds, amounts of water substantially greater than this are desirably avoided as the reaction of water with the halo and/or nitro compound leads to formation of phenolic species and only low molecular weight products are secured. Consequently, in order to secure the high polymers, the system should be substantially anhydrous, and preferably contain less that 0.5 percent by weight water during the reaction.
Preferably, after the desired molecular weight has been attained, the polymer is treated with an activated aromatic halide or an aliphatic halide such as methyl chloride or benzyl chloride, and the like. Such treatment of the polymer converts the terminal hydroxyl groups into ether groups which stabilize the polymer. The polymer so treated has good melt and oxidative stability.
While the carbonate method for preparing the polymer of this invention is simple and convenient, in some cases products of higher molecular weight can be made by the alkali metal hydroxide method. In the alkali metal hydroxide method, described by Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175, a double alkali metal salt of a dihydric phenol is contacted with a dihalobenzenoid compound in the presence of a sulfur containing solvent as herein above defined under substantially anhydrous conditions.
Additionally, the polymers of this invention can be prepared by other methods known in the prior art, in which at least one dihydric phenol and at least one dihalobenzenoid compound are heated, for example, with a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate having a higher atomic number than that of sodium, as described in U.S. Pat. No. 4,176,222.
The molecular weight of the poly(aryl ethers) utilized for manufacturing the devices of the instant invention is indicated by reduced viscosity data in an appropriate solvent such as methylene chloride, chloroform, N,methylpyrrolidone, and the like. The reduced viscosities of the materials, as measured at concentrations of 0.2 g per 100 ml. at 25.degree. C., are at least 0.3 dl/g, preferably at least 0.4 dl/g and, typically, not exceeding about 1.5 dl/g.
The compositions of this invention are prepared by any conventional mixing method. For example, a preferred method comprises mixing the two poly(aryl ether sulfones) in powder or pellets form in an extruder and extruding the mixture into strands, chopping the strands into pellets and molding the pellets into the desired article.
The poly(aryl ether sulfones) of the instant invention allow for the fabrication of medical devices having outstanding stress-crack resistance. These devices can be steam-sterilized under stresses of 500 psi or greater and in the presence of a variety of steam boiler additives. Typical boiler additives designed to reduce corrosion in steam generating systems are amino compounds such as morpholine, hydrazine, N,N-diethylaminoethanol ("NALCO 359" or "BETZ NA-9"), and octadecylamine. Steam sterilization is also possible in the presence of various hospital cleaners and detergents, such as those sold under the tradenames of "Castle 7900" (a sonic cleaner), "Chem Crest 14" (an ultrasonic cleaner), "Tergitol Min Foam 2X" (a non ionic surfactant), and the like.
The materials of the instant invention can include pigments, thermal stabilizers, ultraviolet light stabilizers, and other additives.
The instant poly(aryl ether sulfones) blends are useful for the fabrication of a wide variety of medical devices. They are of particular interest for autoclavable storage trays such as the systems for storage and delivery of sterile surgical instruments (thus eliminating the costs associated with wrapping); in the medical supply industry for shipment and storage of implants, prostheses and other medical devices under sterile conditions; and in many other similar applications.
The compositions of this invention can also be fabricated into any desired shape, i.e., moldings, coatings, films, or fibers. They are particularly desirable for use as electrical insulation for electrical conductors.
These compositions can include mineral fillers such as carbonates including chalk, calcite and dolomite; silicates including mica, talc, wollastonite, silicon dioxide, glass spheres, glass powders; aluminum; clay; quartz; and the like. Also, reinforcing fibers such as fiberglass, carbon fibers, and the like may be used. The compositions may also include additives such as titanium dioxide; thermal stabilizers, ultraviolet light stabilizers, plasticizers, and the like.